The invention relates to residential load shedding.
A typically U.S. house is wired with the capacity to consume approximately 24 kilowatts (kW) of electrical power from an electrical utility company. However, the typical house consumes a much lower annual average power near approximately 1 kW. In order to consume 24 kW of power, nearly all of the electrical appliances and devices in the house would have to be turned on at the same time.
Conventionally, for purposes of receiving electrical power, the house is connected to a power grid that communicates electricity from one or more electrical power plants (hydroelectric or nuclear power plants, for example). However, in the near future, the house may receive partial or total power from its own fuel cell system.
For purposes of generating power, the fuel cell system includes fuel cells that are electrochemical devices that convert chemical energy produced by reactions directly into electrically energy. For example, one type of fuel cell includes a proton exchange membrane (PEM), a membrane that may permit only protons to pass between an anode and a cathode of the fuel cell. At the anode, diatomic hydrogen (a fuel) is oxidized to produce hydrogen protons that pass through the PEM. The electrons produced by this oxidation travel through circuitry that is external to the fuel cell to form an electrical current. At the cathode, oxygen is reduced and reacts with the hydrogen protons to form water. The anodic and cathodic reactions may be described by the following equations:
H2xe2x86x922H++2exe2x88x92
at the anode of the cell, and
O2+4H++4exe2x88x92xe2x86x922H2O
at the cathode of the cell.
Because a single fuel cell typically produces a relatively small voltage (around 1 volt, for example), several serially connected fuel cells may be formed out of an arrangement called a fuel cell stack to produce a higher voltage. The fuel cell stack may include different plates that are stacked one on top of the other in the appropriate order, and each plate may be associated with more than one fuel cell of the stack. The plates may be made from a graphite composite material and include various channels and orifices to, as examples, route the above-described reactants and products through the fuel cell stack. Several PEMs (each one being associated with a particular fuel cell) may be dispersed throughout the stack between the anodes and cathodes of the different fuel cells. The anode and the cathode may each be made out of an electrically conductive gas diffusion material, such as a carbon cloth or paper material, for example.
A fuel cell system typically is sized to efficiently provide a predefined range of output power. In this manner, components of the fuel cell system, such as electrical devices (electrical motors for pumps and blowers, for example) and non-electrical devices (valves, for example), may be sized to produce the predefined range of output power. If the fuel cell system is sized to provide the maximum power (24 kW, for example) that may be consumed by the average house, then the fuel cell system may suffer from inefficiency at the much lower output power that is typically consumed by the house. Additionally, the base cost of such a fuel cell system may be higher due to the system components that are designed to support a larger power output.
In one embodiment of the invention, a system includes a fuel cell subsystem, switches and a controller. The fuel cell subsystem is adapted to provide power that is capable of being consumed by residential loads, and the fuel cell subsystem is sized to provide power up to a first power threshold that is less than a maximum power threshold that is capable of being consumed by the residential loads. The controller is adapted to determine the power that is consumed by the residential loads and based on the determined power, operate the switches to selectively regulate electrical connections between the residential loads and the fuel cell subsystem to keep the power approximately below the first power threshold.
Advantages and other features of the invention will become apparent from the following description, from the drawing and from the claims.